NITROGEN USE EFFICIENCY IN SELECTED RICE (Oryza sativa L.) GENOTYPES GROWN UNDER VARYING WATER REGIMES AND NITROGEN LEVELS

Abstract

A field experiment was conducted in the 2005 wet season at the experimental farm of the International Rice Research Institute (IRRI), Los Banos, Philippines, to assess differences in grain yield (GY) and nitrogen use efficiency (NUE) of a range of vadstosines and to determine important varietal traits that contribute to increase NUE under irrigated and rainfed lowland conditions. Tested were six upland varieties, five rainfed lowland varieties (including three traditional varieties), six irrigated varieties, and two hybrid varieties. The experiment was laid out in a split-plot design with two N treatments (0 and 75 kg N ha‘') in the main plots and nineteen varieties in the subplots with four replications. Highly significant differences among the varieties were observed for GY, harvest index (HI), total plant N uptake (TNU), and internal N use efficiency (IEN) under both water regimes. Irrigated conditions produced on average 55% higher GY than rainfed conditions, indicating considerable water stress in the rainfed treatment.